SUUS is just not SUUS SUUA SUUM. There is a big grid
or masc/fem/neuter deleclining of it thru nominative to
acc, gen, dat and abl. There should also be the plural for it
which is EJUS. I am assuming that EJUS is the declension
for IDEM? This is correct right?

Does anyone know online where i can get the full declension
of SUUS and i am assuming that EJUS is from IDEM

suus, sua, suum declines just like tuus, tua, tuum.. it's a regular 2-1-2 adjective. the nominative plurals are sui, suae, sua. eius is not the plural of suus. eius is in fact the genitive singular of is, ea, id... the third person pronoun (he, she, it). eius is not from idem, idem is an adjective meaning "the same" and is composed of is, ea, id + dem... so the genitive singular is eiusdem.

There's a full table for 1st/2nd declension adjectives here. Just replace the example word with suus. As calvinist said, the plural forms come from the same adjective, and eius is from is/ea/id, not idem.

eius is not reflexive, but suus is. it can be a little confusing at first with these two because in English we can express the reflexive idea without an explicitly reflexive pronoun... for instance: 'He read his book' and 'He read his own book' are both appropriate constructions in English, with both having a reflexive meaning (the book is owned by the person reading it). However, 'He read his book' could also mean 'He read John's book' depending on context. Latin does not have this ambiguity. suus is always used when the reflexive idea is meant, otherwise eius is used... for instance:
Is librum suum legit. "He read his own book."
Is librum eius legit. "He read his (perhaps John or someone else's) book."